Dialkyl esters of n-substituted aspartic acid and method of preparing the same



atented July 20, 1943 m'rso STATES PATENT OFFICE DIALKYIJ ESTERS OF N-SUBSTITUTED ASPARTIC ACID AND METHOD OF PRE- PARING THE SAME Kathryn L. Lynch, Riverside, Conn, assignor to American Cyanamid Company, .New York, N. Y., a corporation of Maine N Drawing.

Claims.

stituted aspartic acid can be prepared simply by 5 reacting with a .primary amine a dialkyl ester of maleic acid in which the alkyl group contains 4 or more carbon atoms. The resulting compounds are surface-active agents of the cation-active type and have been found to possess remarkable b wetting and detergent properties. They are well suited for wetting wool, cotton, cellulose acetate, cellulose nitrate, viscose and similar tlueads and fibres; for demulsification of petroleum emulsions;

in the impregnation of cellulosic fabrics with latex dispersions; dye assistants; in pickling baths; and other uses which will appear evident to those skilled in the. art. A particularly valuable feature of my new compounds is that while they possess marked Wetting properties,-sp1utions thereof have at concentrations in which wetting agents are normally employed non-foaming char acteristics, which is contrary to the normal ,behavior of wetting agents.

I have found that the dialkyl maleates obtained by esterifying maleic acid with alcohols of 4 or more carbon atoms can be condensed with primary alkylolamines or primary hydroxy arylamines and Application September 25, 1940, Serial No. 358,314

hydrocarbon radicals and R is a memberof the group consisting of alkyl and aryl hydrocarbon radicals, the following reaction is found to take Thus, for example, monoethanolamine will react with the diamyl ester of maleic acid to form diamyl N-(Z-hydroxyethyl) aspartate according to the following reaction:

H-COO CHiJHlCHLCHi n H cm 130 cmonm-d-o-oombncmcm In addition to the above condensation there are several side reactions that occur simultaneously butat a much slower rate, the most important being as follows:

o onooocmc cncn cm H0O CHEN (fB.C00 CHii JH.CHiCHa+ k 5 cmbn+ aooimomomon 11.00003, Romain cnconnomomon & nocmcmNHi-- +011, nomcmon their esters and ethers to form new derivatives of N-substituted aspartic acid. When a clialkyl o maleate of the formula: 7

. R1 6 I v (E-C-0 Ra t'i-c-oin in which R1 and R2 are members of the group consisting of hydrogen and alkyl and aryl hydrocarbon radicals, and R3 and R4 are alkyl radi- 5o of hydrogen, acyl radicals, and alkyl and aryl v CH-CONHCHCHlOH A similar reaction involves the conversion of the clialkyl ester of the N-substituted aspartic acid to the corresponding diamide. In addition there appears to be a conversion of maleate ester to fumarate ester occurring-to a small extent. In

members of the series and within a shorter time,-

the unreacted primary amine is removed and the further conversion of the ester to amide is prevented. By this procedure it is possible to obtain yields of from 50% to 75% of the theoretical.

I have found that it is preferable to use primary amines in the above way in the preparation of my new compounds as secondary and tertiary amines do not readily condense at the double bond of maleic esters. The reaction products of maleic esters with secondary amines I consist mostly of amides, imides and aminic esters, as the reaction at the double bond is very 1 slow. The primary amines which I have found useful in the practice of my invention are those having the general formula XO--R-NH2 where X is a member of the group consisting of hydrogen, acyl radicals, and alkyl and aryl hydrocarbon radicals and R is a member of the group consisting of alkyl and aryl hydrocarbon radicals. For example, I have found that I may use monoethanolamine, mono-isopropanolamine, para-aminophenol, or esters or ethers thereof such as amyl oxypropylamine, amyl oxyethylamine, or the acetyl, propionyl or butyryl or benzoylesters of the corresponding alkylolamines.

Dialkyl esters of maleic acid capable of condensing with the above and similar amines to form wetting agents in accordance with my invention have the general formula I II R: o

in which R1 and R2 are members of the group consisting of hydrogen and alkyl and aryl radicals and R3 and R4 are alkyl radicals of 4 or more carbon atoms. R1 and R2 are'non-functional groups; i. e. they take no part in the condensation of the primary amine with the dialkyl ester, but they. influence the wetting properties of the finished product. R3 and R4 may represent the same or different alkyl radicals of 4 or more carbon atoms, as for example R3 may be a hexyl and R4 may be an octyl radical. Specifically R3 and R4 may be n-butyl, amyl, hexyl, octyl, methyl amyl, ethyl hexyl, capryl, decyl, lauryl, stearyl and the like radicals. Specific examples of the dialkyl esters that may be em-- ployed in my invention are diamyl maleate, dibutyi maleate, dicapryl maleate, di-(methyl amyl) maleate, di-(ethyl hexyl) maleate, di-nhexyl maleate, didecyl maleate, dihexyl-aphenyl maleate, dihexyl citraconate, dicapryl pyrocinchonate, hexyl octyl maleate and the like.

In preparing the new compounds of my invention, equimolecular proportions of the dialkyl maleate and primary amine are preferably mixed at room temperatures and the reaction is allowed to proceed for minutes to 3 hours or until the principal reaction approaches the rate of the side reactions, as explained above. The reaction products may then be dissolved in mmeral spirits such as kerosene, toluene, and similar hydrocarbon solvents or, if desired, the reaction may 'be carried out in the presence of the hydrocarbon solvent. Unreacted primary amine is preferably removed by repeated washings with water,

The dialkyl N-substituted aspartate formed in the reaction may be recovered from the" hydrocarbon solution by bubbling dry I-ICl through the water-free solution at 1025 C. until saturated, whereby it is precipitated as the hydrochloride. If desired the precipitate may be recrystallized from dioxane. Another method of recovering the dialkyl N-substituted aspartates consists in extracting the hydrocarbon solution with the theoretical amount of HCl in water to remove the water-soluble hydrochloride. Evaporation of the clear aqueous solution yields the crude hydrochloride, which may be purified by redissolving in water, adding excess NazCOs and extracting the Water-insoluble free base with ethyl ether. The hydrochloride may be precipitated from the ethyl ether by treatment with dry HCl as described above.

For reasons well-known to those skilled in the art amine bases of the type represented by my compounds are generally isolated and handled in the form of the hydrochloride or other acid salts. Consequently, when I speak of my dialkyl N-substituted aspartate I mean to include these compounds in their combined form. It has been found that although it is possible to prepare my compounds in the form of the free base, the hydrochloride is more stable and better suited for handling and storage purposes,

The invention will now be illustrated in greater detail by means of thefollowing specific examples. It should be understood, however, that although these examples may describe in detail some of the more specific features of the invention, they are given primarily by way of illustration and that the invention in its broader aspects is not to be limited thereto.

EXAMPLE 1 512 g. (2 moles) of diamyl maleate and 122 g. (2 moles) of mono-ethanolamine were mixed at 25 C. and the reaction started. Cooling in ice water was required to keep the temperature below 74 C. 1350 cc. of mineral spirits were added and unreacted ethanolamine was removed by.

washing with three 500 cc. portions of water. The diamyl N(2-hydroxyethyl) aspartate formed in the reaction was precipitated as the hydrochloride by bubbling dry HCl through the hydrocarbon solution at 1025 C. until saturated. The precipitated hydrochloride was removed by centrifuging and purified by recrystallization from. dioxane. The product was the hydrochloride of diamyl N(2-hydroxyethyl) aspartate, a white crystalline powder readily soluble in water and melting at 108.5 C.

When mcnopropanolamine was substituted for monoethanolamine in equivalent quantities a product of similar characteristics was obtained. Attempted condensations with diethanolamine, however, were unsuccessful.

The wetting power of diamyl N (Z-hydroxyethyl) aspartate prepared as in Example 1 was measured by the standard Draves sinking time test. This method consists of measuring the time required for a five gram skein of gray 2-ply cotton'yarn to sink in a solution of the wetting agent when the skein, carrying a 1% gram sinker, is held below the surface of the solution by a heavier weight called the anchor. Difierent 1 base. with ethyl ether.

substituted aspartic acid esters of the present in- Dnwes sinking time test at 30 C.

Grams per liter--- 5.0 2.5 1.5 1.25 1.0 0.75 Time in seconds"- 2 3.9 11.5 19.5 32.9 83.0

Dimethyl N-butyl aspartate prepared by a process generally similar to that used in Example l possessed no wetting or foaming properties in water.

EXAMPLE 2 Diamyl maleate and monoethanolamine were reacted as in Example 1. A benzene solution of the free base was washed with water to remove unreacted amine and the solution was then extracted with the theoretical amount of HCl in water to remove the water-soluble hydrochloride. Evaporation of the clear aqueous layer gave an 88% yield of the crude hydrochloride. This was purified by redissolving in water, adding excess NazCOs and extracting the water-insoluble free The product was" then 2; preciptated as the hydrochloride by saturating the solution with gaseous HCl. Its properties were as described in Example 1. I

The purification method of this example may be employed for the recovery of any of the N- vention. Thus, for example, dibutyl N(2-hydroxyethyl) aspartate, diamyl N(hydroxypropyl) aspartate, dihexyl N(p-hydroxyphenyl) aspartate, dicapryl (N-3 -hydroxypropylamino) pyrocinochonate, dihexyl-a-(N-Z-hydroxyethylr amino) a-phenyl succinate, hexyl octyl N(2-hydroxyethyl) aspartate, and like compounds produced according to my invention may be dissolved in benzene, kerosene, toluene or similar hydrocarbon solvents and then washed with waether and then precipitated from the ethyl ether solution with gaseous 1101 as described above.

EXAMPLE 3 30.5 g. (0.5 mole) of monoethanolamine and 142 g. (0.5 mole) of di-methylamyl maleate were mixed at 24 0. During the course of the reaction the temperature rose to 64 C. After a reaction time of about one hour the unreacted amine was removed by washing a mineral spirit solution of the product as in Example 1. saturating the mineral spirit solution with HCl caused the separation of a liquid layer from which dimethylamyl-N-(2-hydroxyethyl) aspartate hydrochloride was separated by extracting with water. The dry product was obtained in 65%, yields, by evaporation of the aqueous solution.

The wetting power of the product was detered by the Draves test with the following re- -stilts: F

Draves sinking time test at 30 0.

-Grams perliter 3.0 2.0 1.5 1.0 0.5 0

Time in seconds 7.6 12.7 18.4 29.2 73.0

EXAMPLE 4 combined as in Example 3. Benzene was added and the unreacted amine extracted with water. The dioctyl N-'(2-hydroxyethyl) aspartate hydrochloride was separated as a syrupy semi-solid which displayed no tendency to crystallize.

A Draves test on the product gave the following result:

Braves sinking time test at 30 C.

EXAMPLE 5 T0568 g. (2 moles) of di-n-hexyl maleat e and 534 g. mineral spirits, were added g. (2 moles+2.5% excess) of monoethanolamine with agitation. The temperature rose to a maximum of 52.5 C. After the react-ion had proceeded for 30 minutes, 200 cc. of wash water were added. This was followed by two 200 cc. washes with water. cc. concentrated HCl were added to the opaque mineral spirit solution with cooling and stirring. The di-n-hexyl N(2-hydr oxyethyl) aspartate hydrochloride which separated from the solution was filtered and dried. The product was obtained in the form of tiny white plate-like crystals of pearlylustre and waxlike feel.

A sample of di-n-hexyl N(2-hydroxyethyl) aspartate hydrochloride gave the following results in the Braves test.

Drapes sinking time test at 30 C. Grams per liter 1.8 0.9 0.72 Time in seconds- 11.2 20.4 31.5 44.4 66.9

' Exsmru: 6 Y

40 g. (0.1 mole) didecyl maleate and 69 (01 mole) monoethanolamine were mixed at 25 C. The temperature rose on stirring to 55 C. The reaction mixture was allowed to cool to 45-50 C. and an equal volume of mineral spirits was added. The solution was washed three times with water to remove excess monoethanolamine and half ester salts formed in the reaction- 8.3 cc. concentrated HCI (0.1 mole) were added to the mineral spirit solution with cooling. A white waxy solid of the hydrochloride of didecyl N(2-hydroxyethyl) aspartate precipitated almost at once.

.The product is soluble in hot water to give opaque foaming solutions which do not precipitate on cooling.

, What I claim is:

1. A process for theproduction oi dialkyl esters of N-substituted aspartic acid of the formula in which R is a member of the'group consisting of alkyl and aryl hydrocarbon radicals, and R3 and R4 are alkyl radicals of at least 4 carbon atoms said esters having wetting-and detergent properties, which comprises reacting a primary amine having the formula HO -R,NHz in which Ris as defined above, with a dialkyl ester of maleic acid of the formula in which Ra and R4 are alkyl radicals of at least 4 carbon atoms. Y

2. A process for the production of dialkyl esters of N-(Z-hydroxyethyl) aspartic acid of the formula in which R3 and R4 are alkyl radicals of at least 4 carbon atoms said esters having wetting and detergent properties, which comprises reacting monoethanolamine with a diaikyl ester of maleic acid of the formula H if in which R: and R4 are alkyi radicals of at least 4 carbon atoms.

3. A process for the production of di-n-hexyi N(Z-hydroxyethyl) aspartate which comprises reacting monoethanolamine with di-n-hexyl maleate. 7

4. A process for the production of diamyl N(2- hydroxyethyl) aspartate which comprises reacting monoethanolamine with diamyl maleate.

5. A process for the production of dihexyl N(2- CERTIFICATE OF CORRECTION.

Patent No 2, 5-2li,7i2.

I It is hereby certified that .error appears of the above numbered patent requiring corre 0nd column, line 55, Example 5, for

" Grams per liter read --G rams per liter and that the said in that the same may-conform to the recor I day '.of September A. D.

Signed and sealed this 7th (Seal) Letters Patent should be read with hydroxypropyl) aspartate which comprises reacting mono-isopropanolamine with dihexyl maleate. 6. A dialkyl ester of N -substituted aspartic acid of the formula i H i Ho-R-N-c-c-mu H-- -C0 R4 1 II H o in which R is a member of the group consisting of 4 carbon atoms said ester h ving wetting and detergent properties. I

8. Dihexyl N-(2-hydroxyethy1) aspartate. 9. Diamyi N-(Z-hydroxyethyi) aspartate. 10. Dihexyl N-(2-hydroxypropyl) aspartate.

KATHRYN L. LYNCH.

July 20 19h;

KATHRYN L. LYNCH.

in the printed specification ction as follows: Page 5, secthis correction there- ;1 of the casein the Patent Office 9 L5- Henry Van 'Arsdale .Acting' Comissioner of Patents.

CERTIFICATE OF c'oRREcT'Io'u. Patent No. 252L712. July 20, 1915.-

- KATHRYN L. LYNCH.

' It is hereby certified that .error appears in the printed specification of the above numbered patent requiring correction as follows: Page 5, sec- 0nd column, line 55, Example 5, for

'' Grams per liter 1. 0.9 0.721

read

"Grams per liter 1.0 0.5 0.2 0.l25-;

Q and that thesaid Letters Patent should be'read ivith this correction therein that the same mayconform to the record of the casein the'Patent Office.

Signed and sealed this 7th day 101 September, A. D. 1915.

Henry Van-Arsda1e, (Seal) .Acting Commissioner of Patents. 

